My opinion is:
With 100 very similar products, show many on a page; you need users to be able to compare relatively quickly without getting frustrated. [e.g. ebay]
With 100 quite different products, you should have sub-categories leading to pages of about 10 products each.
I've not tested it but I base it on showing the visitor only the product options they are interested in. If I want a widget, show me a page of a dozen widgets rather than page with six-dozen general gadgets, of which a dozen are widgets.
I think Hubie is asking how many to show per page within a related category. I think the number might be related to how big the thumbnails are. Small thumbnails and you can probably do a comfortable 12-18 per page. Large thumbnails will limit you down to 6-12 per page. I think the key is not to have a long vertical scrollbar if you can help it.
if you can show the list quickly in an organized manner, I enjoy browsing 50 items a page
IMO, load time and length of page are the deciding factors. I go 1.5 - 2 screens deep at 1040 rez, with two columns of products that gives me 30 per page, which doesn't overload the user and doesn't put them into tombstone scrolling.
Most of clients favor under 20 per page, and then paginate the rest at the bottom.
I've done some A/B testing. I didn't try anything dramatic like 50, for small changes I didn't get a big impact.
I love sites that by default show 12-20 items on a page, but also have an option at the top right to either show 100 per page or "Show All." Since I've got a fast connection, I can handle "Show All," but I know that a large portion of people worldwide definitely can't. If you're able to have a "Show All" or "100 per page" option, go for it. If not, I'd stick with 12-20, or even more or less based on load time.
I do 12 floated divs because I think it's the most flexible because it has three consecutive factors: 2, 3, and 4.
So make the div's width large enough to fit 4 across your normal large screen and then for users with smaller monitors it will fit either 2 or 3.
That will make an even 3, 4, or 6 rows depending on the size of the user's monitor.
Idk if I look into it too much, but that's just my theory :-o
Make that four consecutive factors if you include 1 :x. User's with REALLY small monitors can get 1x12 :}
I've never had an opportunity to do A/B testing on this myself -- but as a user and an online shopper I know what makes me crazy: When I see that there are 50, or 80, or more products in that category, but the site won't allow me to view more than a handful at a time. Since I've had broadband, I would much rather "show all 100 products" than click "Next 6" 15 or 20 times.
Selecting a reasonable default setting is important, but if you have any large categories with lots of products, user options are just as important, IMO.